With the recent trends in legalisation and with the transition of illegal drug markets to the internet, much more detailed information about the price and quality of cannabis is now available, making an analysis of the determinants of prices easier. This column analyses data collected over a two-week period in 2015 from a dark web marketplace, which details about 500 cannabis prices from around 140 sellers in 18 countries. It concludes that the internet-based cannabis market is characterised by monopolistic competition, where many sellers offer differentiated products with quality variation causing dispersion of cannabis prices.

There is a robust positive association between support for cannabis liberalisation and cannabis use, but it is unclear whether users have discovered that cannabis is innocuous, or if these types are inherently more liberal regarding drug policy. This column exploits variations in opinion between current and former cannabis users to work towards establishing causality. Results suggest that supporters of liberalisation are speaking from experience rather than personal interest.

The decriminalisation of cannabis is a policy that divides policymakers sharply. This column uses evidence from the Netherlands to show a positive connection between early cannabis use and easy access to cannabis through coffeeshops. The policy implications, however, require further research. Closing coffeeshops could result in some potential users searching in the black market where hard drugs are available as well.

In many Western countries, between one quarter and one third of the population admit to having used cannabis at least once in their lives – according to the official statistics. This column provides an in-depth review of existing economic, social, and media evidence for and against legalisation. It concludes that although there is of course uncertainty surrounding the long-term implications, prohibition is not working and it is time to legalise.

Imran Rasul of University College London talks to Romesh Vaitilingam about his research with Jerome Adda and Brendon McConnell on the effects of a localized policing experiment that decriminalized cannabis possession in the London borough of Lambeth between 2001 and 2002. The interview was recorded at the annual congress of the European Economic Association in Glasgow in August 2010.

There is growing evidence of a link between mental health problems and cannabis use. Is it causal? This column shows that cannabis use, particularly frequent use, does have an adverse effect on mental health. Unobserved factors that make individuals more likely to use cannabis do also make them more susceptible to mental illness, but using marijuana has an additional causal impact.